//==========================================
// 几何星空连线背景
//==========================================

export function useStarLink() {
    // 可调参数
    var BACKGROUND_COLOR = "#f5f5f5";   // 背景颜色
    var POINT_NUM = 100;                        // 星星数目
    var POINT_COLOR = "rgba(13,139,251,0.7)";  // 点的颜色
    var LINE_LENGTH = 10000;                    // 点之间连线长度(的平方)

    // 创建背景画布
    var cvs = document.createElement("canvas");
    cvs.width = window.innerWidth;
    cvs.height = window.innerHeight;
    cvs.style.cssText = "\
    position:fixed;\
    top:0px;\
    left:0px;\
    z-index:-1;\
    opacity:1.0;\
    ";
    document.body.appendChild(cvs);

    var ctx = cvs.getContext("2d");

    var startTime = new Date().getTime();

    //随机数函数
    function randomInt(min, max) {
        return Math.floor((max - min + 1) * Math.random() + min);
    }

    function randomFloat(min, max) {
        return (max - min) * Math.random() + min;
    }

    //构造点类
    function Point() {
        this.x = randomFloat(0, cvs.width);
        this.y = randomFloat(0, cvs.height);

        var speed = randomFloat(0.3, 1.4);
        var angle = randomFloat(0, 2 * Math.PI);

        this.dx = Math.sin(angle) * speed;
        this.dy = Math.cos(angle) * speed;

        this.r = 1.2;

        this.color = POINT_COLOR;
    }

    Point.prototype.move = function () {
        this.x += this.dx;
        if (this.x < 0) {
            this.x = 0;
            this.dx = -this.dx;
        } else if (this.x > cvs.width) {
            this.x = cvs.width;
            this.dx = -this.dx;
        }
        this.y += this.dy;
        if (this.y < 0) {
            this.y = 0;
            this.dy = -this.dy;
        } else if (this.y > cvs.height) {
            this.y = cvs.height;
            this.dy = -this.dy;
        }
    }

    Point.prototype.draw = function () {
        ctx.fillStyle = this.color;
        ctx.beginPath();
        ctx.arc(this.x, this.y, this.r, 0, Math.PI * 2);
        ctx.closePath();
        ctx.fill();
    }

    var points = [];

    function initPoints(num) {
        for (var i = 0; i < num; ++i) {
            points.push(new Point());
        }
    }

    var p0 = new Point(); //鼠标
    p0.dx = p0.dy = 0;
    var degree = 2.5;
    document.onmousemove = function (ev) {
        p0.x = ev.clientX;
        p0.y = ev.clientY;
    }
    document.onmousedown = function (ev) {
        degree = 5.0;
        p0.x = ev.clientX;
        p0.y = ev.clientY;
    }
    document.onmouseup = function (ev) {
        degree = 2.5;
        p0.x = ev.clientX;
        p0.y = ev.clientY;
    }
    window.onmouseout = function () {
        p0.x = null;
        p0.y = null;
    }

    function drawLine(p1, p2, deg) {
        var dx = p1.x - p2.x;
        var dy = p1.y - p2.y;
        var dis2 = dx * dx + dy * dy;
        if (dis2 < 2 * LINE_LENGTH) {
            if (dis2 > LINE_LENGTH) {
                if (p1 === p0) {
                    p2.x += dx * 0.03;
                    p2.y += dy * 0.03;
                } else return;
            }
            var t = (1.05 - dis2 / LINE_LENGTH) * 0.2 * deg;
            ctx.strokeStyle = "rgba(13,139,251," + t + ")";
            ctx.beginPath();
            ctx.lineWidth = 1.5;
            ctx.moveTo(p1.x, p1.y);
            ctx.lineTo(p2.x, p2.y);
            ctx.closePath();
            ctx.stroke();
        }
        return;
    }

    //绘制每一帧
    function drawFrame() {
        cvs.width = window.innerWidth;
        cvs.height = window.innerHeight;
        ctx.fillStyle = BACKGROUND_COLOR;
        ctx.fillRect(0, 0, cvs.width, cvs.height);

        var arr = (p0.x == null ? points : [p0].concat(points));
        for (var i = 0; i < arr.length; ++i) {
            for (var j = i + 1; j < arr.length; ++j) {
                drawLine(arr[i], arr[j], 1.0);
            }
            arr[i].draw();
            arr[i].move();
        }

        window.requestAnimationFrame(drawFrame);
    }

    function init() {
        initPoints(POINT_NUM);
        drawFrame();
    }

    return {
        init: init
    }
}